/*
 *  linux/init/main.c
 *
 *  (C) 1991  Linus Torvalds
 */

#define __LIBRARY__
#include <unistd.h>
#include <time.h>

/*
 * we need this inline - forking from kernel space will result
 * in NO COPY ON WRITE (!!!), until an execve is executed. This
 * is no problem, but for the stack. This is handled by not letting
 * main() use the stack at all after fork(). Thus, no function
 * calls - which means inline code for fork too, as otherwise we
 * would use the stack upon exit from 'fork()'.
 *
 * Actually only pause and fork are needed inline, so that there
 * won't be any messing with the stack from main(), but we define
 * some others too.
 */
static inline _syscall0(int,fork)
static inline _syscall0(int,pause)
static inline _syscall1(int,setup,void *,BIOS)
static inline _syscall0(int,sync)

#include <linux/tty.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <asm/system.h>
#include <asm/io.h>

#include <stddef.h>
#include <stdarg.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>

#include <linux/fs.h>

#include <string.h>

static char printbuf[1024];

extern char *strcpy();
extern int vsprintf();
extern void init(void);
extern void blk_dev_init(void);
extern void chr_dev_init(void);
extern void hd_init(void);
extern void floppy_init(void);
extern void mem_init(long start, long end);
extern long rd_init(long mem_start, int length);
extern long kernel_mktime(struct tm * tm);

static int sprintf(char * str, const char *fmt, ...)
{
	va_list args;
	int i;

	va_start(args, fmt);
	i = vsprintf(str, fmt, args);
	va_end(args);
	return i;
}

/*
 * This is set up by the setup-routine at boot-time
 */
#define EXT_MEM_K (*(unsigned short *)0x90002)
#define CON_ROWS ((*(unsigned short *)0x9000e) & 0xff)
#define CON_COLS (((*(unsigned short *)0x9000e) & 0xff00) >> 8)
#define DRIVE_INFO (*(struct drive_info *)0x90080)
#define ORIG_ROOT_DEV (*(unsigned short *)0x901FC)
#define ORIG_SWAP_DEV (*(unsigned short *)0x901FA)

/*
 * Yeah, yeah, it's ugly, but I cannot find how to do this correctly
 * and this seems to work. I anybody has more info on the real-time
 * clock I'd be interested. Most of this was trial and error, and some
 * bios-listing reading. Urghh.
 */

#define CMOS_READ(addr) ({ \
outb_p(0x80|addr,0x70); \
inb_p(0x71); \
})

#define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10)

static void time_init(void)
{
	struct tm time;

	do {
		time.tm_sec = CMOS_READ(0);
		time.tm_min = CMOS_READ(2);
		time.tm_hour = CMOS_READ(4);
		time.tm_mday = CMOS_READ(7);
		time.tm_mon = CMOS_READ(8);
		time.tm_year = CMOS_READ(9);
	} while (time.tm_sec != CMOS_READ(0));  /* CMOS读取很慢，这里确保一秒内读完 */
	BCD_TO_BIN(time.tm_sec);
	BCD_TO_BIN(time.tm_min);
	BCD_TO_BIN(time.tm_hour);
	BCD_TO_BIN(time.tm_mday);
	BCD_TO_BIN(time.tm_mon);
	BCD_TO_BIN(time.tm_year);
	time.tm_mon--;          /* 月份0-11 */
	startup_time = kernel_mktime(&time);    /* 计算从1970.1.0起到开机经过的秒数 */
}

static long memory_end = 0;     /* 物理内存容量(字节数) */
static long buffer_memory_end = 0;  /* 高速缓冲区末端地址 */
static long main_memory_start = 0;  /* 主内存区开始的位置 */
static char term[32];   /* 中断设置字符串（环境参数） */

static char * argv_rc[] = { "/bin/sh", NULL };  /* 读取并执行/etc/rc文件时所使用的命令行参数 */
static char * envp_rc[] = { "HOME=/", NULL ,NULL }; /* 环境参数 */

static char * argv[] = { "-/bin/sh",NULL }; /* 远程登录的命令行参数 */
static char * envp[] = { "HOME=/usr/root", NULL, NULL }; /* 环境参数 */

struct drive_info { char dummy[32]; } drive_info;   /* 硬盘参数表信息 */

void main(void)		/* This really IS void, no error here. */
{			/* The startup routine assumes (well, ...) this */
/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
 	ROOT_DEV = ORIG_ROOT_DEV;   /* 根文件系统设备号 */
 	SWAP_DEV = ORIG_SWAP_DEV;   /* 交换设备号 */
	sprintf(term, "TERM=con%dx%d", CON_COLS, CON_ROWS);
	envp[1] = term;	
	envp_rc[1] = term;
 	drive_info = DRIVE_INFO;    /* 硬盘参数表 */
	memory_end = (1<<20) + (EXT_MEM_K<<10); /* 内存大小=1Mb+扩展内存(k)*1024 */
	memory_end &= 0xfffff000;   /* 忽略不到4Kb(1页)的内存数 */
	if (memory_end > 16*1024*1024)
		memory_end = 16*1024*1024;  /* 内存超过16M，只按16M */
	if (memory_end > 12*1024*1024) 
		buffer_memory_end = 4*1024*1024;    /* 内存大于12M，缓冲区末端=4Mb */
	else if (memory_end > 6*1024*1024)      /* 内存大于6M,缓冲区末端=2Mb */
		buffer_memory_end = 2*1024*1024;
	else                                    /* 否则，缓冲区末端=1Mb */
		buffer_memory_end = 1*1024*1024;
	main_memory_start = buffer_memory_end;  /* 主内存起始位置=缓冲区末端 */
#ifdef RAMDISK
	main_memory_start += rd_init(main_memory_start, RAMDISK*1024);  /* 如果定义了RAMDISK，则在主内存区初始化虚拟盘，主内存减少 */
#endif
	mem_init(main_memory_start,memory_end); /* 主内存区初始化 */
	trap_init();            /* 陷阱门（硬件中断向量）初始化,就是设置中断描述符表 */
	blk_dev_init();         /* 块设备初始化 */
	chr_dev_init();         /* 字符设备初始化,啥都没做 */
	tty_init();             /* tty初始化 */
	time_init();            /* 设置开机启动时间 */
	sched_init();           /* 调度程序初始化（加载任务0的tr,ldtr）*/
	buffer_init(buffer_memory_end); /* 缓冲管理初始化，建内存链表等 */
	hd_init();              /* 硬盘初始化 */
	floppy_init();          /* 软驱初始化 */
	sti();                  /* 所有初始化工作都做完喽，开启中断 */
	move_to_user_mode();    /* 移到用户模式下执行。通过在堆栈中设置的参数，利用中断返回指令启动任务0执行 */
	if (!fork()) {		/* we count on this going ok */
		init();
	}
/*
 *   NOTE!!   For any other task 'pause()' would mean we have to get a
 * signal to awaken, but task0 is the sole exception (see 'schedule()')
 * as task 0 gets activated at every idle moment (when no other tasks
 * can run). For task0 'pause()' just means we go check if some other
 * task can run, and if not we return here.
 */
	for(;;)
		__asm__("int $0x80"::"a" (__NR_pause):"ax");
}

static int printf(const char *fmt, ...)
{
	va_list args;
	int i;

	va_start(args, fmt);
	write(1,printbuf,i=vsprintf(printbuf, fmt, args));
	va_end(args);
	return i;
}

void init(void)
{
	int pid,i;

	setup((void *) &drive_info); /* 读取硬盘参数包括分区表信息并加载虚拟盘（若存在的话）和安装根文件系统设备 */
	(void) open("/dev/tty1",O_RDWR,0); /* 第一次打开文件，返回的文件句柄肯定是0，前面的void强制无返回值 */
	(void) dup(0);  /* 复制文件句柄，得到句柄1，对应stdout */
	(void) dup(0);  /* 复制文件句柄，得到句柄2，对应stderr */
	printf("%d buffers = %d bytes buffer space\n\r",NR_BUFFERS,
		NR_BUFFERS*BLOCK_SIZE);
	printf("Free mem: %d bytes\n\r",memory_end-main_memory_start);
	if (!(pid=fork())) { /* 创建进程2 */
		close(0);   /* 关闭句柄0 */
		if (open("/etc/rc",O_RDONLY,0)) /* 打开/etc/rc文件，会重新得到句柄0，把标准输入stdin重定向到该文件 */
			_exit(1);
		execve("/bin/sh",argv_rc,envp_rc);  /* 将进程自身替换成/bin/sh程序，然后执行该程序，shell执行的就是/etc/rc文件中的命令，非交互式执行的shell，执行完进程2就退出了 */
		_exit(2);
	}
	if (pid>0)
		while (pid != wait(&i)) /* 父进程等待子进程结束，wait返回值不等于子进程号，继续等待 */
			/* nothing */;
	while (1) {
		if ((pid=fork())<0) {
			printf("Fork failed in init\r\n");
			continue;
		}
		if (!pid) { /* 子进程 */
			close(0);close(1);close(2); /* 关闭文件句柄0，1，2 */
			setsid();   /* 创建新的会话，并设置进程组号 */
			(void) open("/dev/tty1",O_RDWR,0);  /* 打开/dev/tty1 */
			(void) dup(0);  /* 复制得到1 */
			(void) dup(0);  /* 复制得到2 */
			_exit(execve("/bin/sh",argv,envp)); /* 执行/bin/sh */
		}
		while (1)   /* 等待子进程结束 */
			if (pid == wait(&i))    /* 子进程结束之后，到211行在创建子进程 */
				break;
		printf("\n\rchild %d died with code %04x\n\r",pid,i);
		sync(); /* 同步操作，刷新缓冲区 */
	}
	_exit(0);	/* NOTE! _exit, not exit() */   /* _exit调用sys_exit系统调用，exit调用库函数，会做清理工作，然后调用_exit */
}
